Persistent environmental pollutants from domestic and industrial waste and pesticides could be changing the ratio of sex chromosomes in human sperm, according to new Swedish research.

Andrologist, Professor Aleksander Giwercman, of Malmö University Hospital, Lund University, and team report their findings online this week in the journal Human Reproduction.

The researchers found that Swedish fishermen exposed to high levels of persistent organochlorine pollutants (POPs) have a higher proportion of the male Y chromosomes in their sperm

"The more exposed the fishermen were to the chemicals the more Y chromosomes we found," says Giwercman.

The fishermens' age, smoking habits and hormone levels were not associated with the increase in Y chromosomes.

An egg fertilised by a Y chromosome sperm will produce a boy while an X chromosome sperm results in a girl.

But the researchers do not know whether the increase in numbers of Y chromosomes mean more boys than girls will be born.

They also do not know the mechanism by which the chemicals could be increasing the number of Y chromosomes.

Banned pollutants

Dioxin, DDT and PCBs, which were used in industrial and commercial applications before being banned, are examples of organochlorine pollutants.

Giwercman and his team studied semen from 149 fishermen who were exposed to two particular POPs, CB-153 and DDE, possibly by eating contaminated fatty fish from areas such as the Baltic Sea.

"To our knowledge, this is the first study to show that the distribution of the sex chromosomes in sperm can be affected by exposure to POPs," says Giwercman.

When they compared the 20% of fishermen with the highest exposure to the pollutants with the 20% with the lowest, they found an increase in Y chromosome sperm in the higher group.

"This is more evidence that chemicals, which everyone is exposed to, have an effect on the function of the reproductive system," says Giwercman.

Earlier studies have suggested that exposure to different chemicals in the environment could change the ratio of boys to girls being born.

Giwercman adds that the quality of the sperm is also affected by the pollutants.

In a separate study, also published by the journal, Danish researcher Dr Niels Jørgensen, of the Rigshospitalet in Copenhagen, and team, suggest that a larger than expected number of male babies born with undescended testes in Lithuania could also be linked to environmental factors.

"We need to look more closely at the role of environmental factors, including those that can disrupt the hormone system, and the role of genetics, lifestyle and other factors," says Jørgensen.